1. Field of the Invention
The present invention generally concerns electronic voltage regulators, such as those found in motor vehicles, that serve to regulate the current in the field winding of an alternator in accordance with the level of a direct current, battery, voltage that is maintained by the alternator. The present invention particularly concerns modifications to an electronic voltage regulator that is already improved so as to protect against (i) induced failure due to overload, and also, separately and additionally, (ii) induced failure due to loss of a reference voltage.
The present invention still more particularly concerns both (i) an improvement to a particular electronic voltage regulator overload-protection circuit of the prior art so as to permit a voltage regulator having this improvement circuit to reliably conduct the high field currents that are associated with high alternator current outputs, and, separately and severally, a (ii) an improvement to the noise figure of an electronic voltage regulator.
2. Description of the Prior Art
The present patent application concerns improvements to electronic voltage regulators in general, and in particular concerns improvements that are usefully incorporated in the ELECTRONIC VOLTAGE REGULATOR PROTECTED AGAINST FAILURE DUE TO OVERLOAD, OR DUE TO LOSS OF A REFERENCE VOLTAGE that is taught in U.S. Pat. No. 5,325,044 issued Jun. 28, 1994, to the selfsame Luis Bartol who is a co-inventor in the present application. The contents of the related patent are incorporated herein by reference.
In the prior patent an electronic voltage regulator, particularly a regulator serving to regulate the voltage of a field coil of an alternator within a motor vehicle, is protected against catastrophic failure of its output transistor due to a short-circuit overload by action of a direct current (d.c.) electrical path within the circuit of the regulator. This d.c. path, preferably a single diode, discharges an existing capacitor present within an alternating current (a.c.) feedback path between the regulator's output transistor and its error amplifier stage. This discharge causes the output transistor to break into a safe, and non-destructive, oscillation for the duration of any overload.
The same electronic voltage regulator is further, optionally, protected against a catastrophic failure of its output transistor due to a loss of the reference voltage supplied to the regulator. This protection is obtained by action of yet another, second, direct current (d.c.) electrical path. This second d.c. path, preferably a single resistor, serves, upon loss of a reference voltage to the voltage regulator, to couple voltage produced by the magnetic field within the field winding of the alternator back to the error amplifier stage of the regulator. This coupled voltage causes the error amplifier stage to, in turn, drive the regulator's output bipolar transistor to a condition where, by action of the first and the second paths, the bipolar transistor is safely maintained in an oscillatory condition until the reference voltage is restored.
The advanced operation of this voltage regulator protected both against failure (i) due to overload, and (ii) due to loss of a reference voltage, has been, and continues to be, proven successful both in the market and in real-world use since the 1991 filing of the related application. Quite simply, and as is explained in the related patent, a voltage regulator so protected will survive without harm two common external conditions that are causative of the catastrophic failure of any voltage regulator not so protected.
However, certain high-output configurations of the protected voltage regulator--such as are particularly used in heavy duty applications such as trucks--have shown to exhibit some sensitivity to "pulsing" or "hunting" upon the occasion(s) of high alternator field drive currents. This sensitivity is due to false activation of the overload protection circuitry. Essentially the overload-protected voltage regulator has difficulty discriminating between a total short circuit and the current that would flow in the alternator field winding upon the occasion of a very high alternator current of more than, typically, one hundred amperes (100 Amp.).
Additionally, the previous invention does nothing to improve the noise figure of the regulation. If the quality of the regulation can be improved in vehicular applications, and the vehicle primary power bus made to exhibit lower noise under diverse conditions and at frequencies ranging from conducted broadband to radio, then the cost of noise filtration in the electronic devices, such as radios and computers, that derive their primary power from the vehicle bus might be lessened.
Accordingly, and considering that the design of voltage regulators is still (circa 1995) an art as well as a science, various things that can be cost-effectively done to improve overall voltage regulation performance are worthy of evaluation, and are potentially desirable.